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Title: Dynamics of the lignin glass transition

The dynamics of lignin, a complex and heterogeneous major plant cell-wall macromolecule, is of both fundamental and practical importance. Lignin is typically heated to temperatures above its glass transition to facilitate its industrial processing. Here, we performed molecular dynamics simulations to investigate the segmental (α) relaxation of lignin, the dynamical process that gives rise to the glass transition. It is found that lignin dynamics involves mainly internal motions below T g, while segmental inter-molecular motions are activated above T g. The segments whose mobility is enhanced above T g consist of 3–5 lignin monomeric units. The temperature dependence of the lignin segmental relaxation time changes from Arrhenius below T g to Vogel–Fulcher–Tamman above T g. This change in temperature dependence is determined by the underlying energy landscape being restricted below T g but exhibiting multiple minima above T g. The Q-dependence of the relaxation time is found to obey a power-law up to Q max, indicative of sub-diffusive motion of lignin above T g. Temperature and hydration affect the segmental relaxation similarly. Increasing hydration or temperature leads to: (1) the α process starting earlier, i.e. the beta process becomes shortened, (2) Q max decreasing, i.e. the lengthscale above which subdiffusionmore » is observed increases, and (3) the number of monomers constituting a segment increasing, i.e. the motions that lead to the glass transition become more collective. The above findings provide molecular-level understanding of the technologically important segmental motions of lignin and demonstrate that, despite the heterogeneous and complex structure of lignin, its segmental dynamics can be described by concepts developed for chemically homogeneous polymers.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics (CMB); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Biochemistry and Cellular and Molecular Biology; Giresun Univ. (Turkey). Dept. of Physics
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). UT/ORNL Center for Molecular Biophysics (CMB); Univ. of Tennessee, Knoxville, TN (United States). Dept. of Biochemistry and Cellular and Molecular Biology
Publication Date:
Grant/Contract Number:
AC05-00OR22725; FWP ERKP752; AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 20; Journal Issue: 31; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division
Contributing Orgs:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; 09 BIOMASS FUELS
OSTI Identifier:
1471833
Alternate Identifier(s):
OSTI ID: 1461709

Vural, Derya, Smith, Jeremy C., and Petridis, Loukas. Dynamics of the lignin glass transition. United States: N. p., Web. doi:10.1039/C8CP03144D.
Vural, Derya, Smith, Jeremy C., & Petridis, Loukas. Dynamics of the lignin glass transition. United States. doi:10.1039/C8CP03144D.
Vural, Derya, Smith, Jeremy C., and Petridis, Loukas. 2018. "Dynamics of the lignin glass transition". United States. doi:10.1039/C8CP03144D.
@article{osti_1471833,
title = {Dynamics of the lignin glass transition},
author = {Vural, Derya and Smith, Jeremy C. and Petridis, Loukas},
abstractNote = {The dynamics of lignin, a complex and heterogeneous major plant cell-wall macromolecule, is of both fundamental and practical importance. Lignin is typically heated to temperatures above its glass transition to facilitate its industrial processing. Here, we performed molecular dynamics simulations to investigate the segmental (α) relaxation of lignin, the dynamical process that gives rise to the glass transition. It is found that lignin dynamics involves mainly internal motions below Tg, while segmental inter-molecular motions are activated above Tg. The segments whose mobility is enhanced above Tg consist of 3–5 lignin monomeric units. The temperature dependence of the lignin segmental relaxation time changes from Arrhenius below Tg to Vogel–Fulcher–Tamman above Tg. This change in temperature dependence is determined by the underlying energy landscape being restricted below Tg but exhibiting multiple minima above Tg. The Q-dependence of the relaxation time is found to obey a power-law up to Qmax, indicative of sub-diffusive motion of lignin above Tg. Temperature and hydration affect the segmental relaxation similarly. Increasing hydration or temperature leads to: (1) the α process starting earlier, i.e. the beta process becomes shortened, (2) Qmax decreasing, i.e. the lengthscale above which subdiffusion is observed increases, and (3) the number of monomers constituting a segment increasing, i.e. the motions that lead to the glass transition become more collective. The above findings provide molecular-level understanding of the technologically important segmental motions of lignin and demonstrate that, despite the heterogeneous and complex structure of lignin, its segmental dynamics can be described by concepts developed for chemically homogeneous polymers.},
doi = {10.1039/C8CP03144D},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 31,
volume = 20,
place = {United States},
year = {2018},
month = {7}
}

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